Prevention of reverse flow in water supply systems



Dec. 23, 1941. NORTHQN 2,267,354

' PREVENTION OF REVERSE FLOW IN WATER SUPPLY SYSTEMS Filed Feb. 2, 1940 2 Sheets-Sheet 1 Dec. 23, 1941. NORTHQN 7 2,267,354

PREVENTION OF REVERSE FLOW IN WATER SUPPLY SYSTEMS Filed Feb. 2, 1940 2 Sheets-Sheet 2 1 F/GHZ Patented Dec. 23, 1941 PREVENTION OF REVERSE FLOW WATER SUPPLY SYSTEMS 1 Louis Irving North'on, Washington, D. ,0.

Application February 2, 1940; Serial-N0.-317,020 5 Claims.- (01. 137-79) f The present invention-relates to improvements in Water supply systems and-has reference more particularly to an arrangement *for preventing" the flow of liquid in other than the designed direction and thereby preventingback siphonage and reverse flow from occurring.

This application is a continuation in part of I my copending application, Serial- Number 137,- 232, filed April 16, 1937, nowPatent No. 2,205,305,- granted June 18; 1940;

One of the important objects of the presentinvention is to provide an arrangement-whichwill prevent backsiphonage, irrespective of pressure variations and conditionstha-t-may occur in the water supply system, and further with out the use of any mechanical means orrhoving parts.

A still further object of the invention resides in the provision of' an arrangement of'theabove mentioned character which can be readily and.

easily installed in -a water supply system without necessitating any material alterations in the system, and which-willat all times be positive and eificient in carrying out the purposes for which the same has been designed.

An important, though not the only application of the invention will be in conjunction with water When applied-to such systems, my invention will prevent reverse flow and back supply systems,

siphonage from cross connected plumbing fix tures, etc-., through supply branches toward the supply riser.

According to the present invention, means is provided to prevent the occurrence of any sub- I stantial sub-atmospheric pressure (vacuum) in water supply risers, etc. This arrangement is tobe distinguished from arrangements in which atmospheric air is introduced only after the occurrence of a partial vacuum, or of a vacuum at its critical. pressure, and, ithereiorgafter back siphonage has or could have occurredgas where unreliable vacuum breakers and the like 7 are employed. For accepted formula-of critical pressure of vacuum, see my Patent No. 2,205,305,,

page 2, lines '70 to 74, inclusive.

Other objects andadvantages of the presentinventionwillbecome apparent from the accom,-- panying drawings and the following description,

In the drawings, wherein like reference char acters designate corresponding parts Figure 1 represents a schematic representation of a part of water supply system (riser and sup-. ply branches) embodying the invention, and.

Figure 2 is a similar schematic representation of a part of a water supplysystemindicatinsn the usual and customary practice of installation j of the riser and branches, with the addition of a liquid seal for the uppermost receptacle.

Inythedrawings, with reference more particularlyto Figure l," the numeral 8 designates the usual riser 'whichsupplies water in any up-feed or in any downfeed water supply system, to the branches leadingto various discharge outlets and plumbing fixtures located on the various. floors of a building. In accordance with build ing constructionand design conditions, the various supply branches are usually located below the finished ceiling or in the floor, inorder to.

avoid-door or window crossings with such supply branches;

It-is also known in practice, that a supply riser may supply the water totwo bath roomsor kitchens," especially when the riserjis located in thepartition between two dwellings. In such instances; the supply branches are doubled on each floor in order to supply hotandcold Water to both dwellings.

A liquid seal, shown generally at l,is asso-, ciated With the upper open end 9 of the riser] 8 and ismore specifically disclosed in vmy applicjaa tion,SerialNumber137,232.: The liquid sealil,

includes a shellor jacket that surrounds the upper end portionof the riser8 in spaced rela tion thereto, the lower end of this shell or jacket] being connected'to the adjacent portion of.the

riserto provide a closed bottom for said jacket. j The upper end of this shell 'or jacket is openanol extends above the open upper end .of the riser v and has a vent pipe or opening ll] extending up: Wardly therefromfor supplyingair to the seal,

and riser 8, when the pressure, due'to various, reasons, ceases in the riser.

The uppermost receptacle 5 represents any 1 plumbing fixture and theconduit or branch 2 3 affords communication between the lower portion (discharge outlet) of the liquid seal I and The height of the maximum Water level of the receptacle 5 above the conduit the receptacle 5.

or branch 2 isindicatedin the, drawing by ha and the top. end of the submerged supply riser (submerged in, the liquid seal l)' is1 indicated.

y i. Sincethe top of the submerged riser inthe liquid seal 1 is considerably higher than the maximum height of the water level of the receptacle 5, consequently,fthe top of the submerged riser, 8 can never be overflooded with water in case of 5 a total pressure drop in the supply riser.

From theflforegoing it is clearly seen that whena total-pressure drop occurs'in the riser 8,;

consequently first, at the top of the submerged riser, due to the height of the water column in shell I I, a positive pressure must exist at the bottom of branch 2 that is directly connected to the outer shell of the liquid seal I. This height being in excess of ha therefor, due to prevailing hydrostatic pressure, flow must occur through supply branch 2 toward the receptacle 5. The excess pressure created by the constant height of the liquid seal is indicated by ha, or the excess pressure h2=hl-hR.

In case of a partial or a total pressure drop, the supplied atmospheric air is present in the extended part of the air supply pipe l (air inlet or air supply opening) and when the pressure ceases in riser 8, the down falling water column will be followed by the supplied atmospheric air.

The direction of flow of the atmospheric air is indicated by the arrows and the atmospheric air itself exerts its pressure on the surface of the water in the various receptacles, just the same as the same atmospheric pressure exerts its pressure on the surface of water in water seal I at the height marked, ha, thereby creating the absolutely necessary pressure equilibrium.

The velocity of the atmospheric air flow is always the same as the velocity of the down falling water column in the riser 8. The water must evacuate the riser first, and only then, can the inflowing atmospheric air replace the water in the riser in order to create atmospheric air conditions in the riser, thereby preventing such vacuum formations, which vacuum would ever be able to lift up the water column hi. Since in a case of a total pressure drop the maximum height of the water line he in shell H is entirely separated from the riser 8 by the outer shell ll of the water seal I, therefore an entirely free air supply port is secured at the open upper end 9 of the riser and the atmospheric air will flow freely into the submerged riser 8 regardless of the source of the supplied atmospheric air.

At the same time the supplied atmospheric air will exert its pressure on the surface of the water in the shell or jacket ll of the water seal and the same atmospheric pressure-will exert its pressure on the surface of the water in the receptacle 5. This will result in the pressure conditions being placed in equilibrium, hence no vacuum formation, much less back siphonagewill or could occur in the upper part (top floor) of the water supply system.

In order to secure the same safe water supply conditions at the lower floors of a building, it is necessary to install at each floor, a branch supply conduit in the form of a loop, designated at 3-B which extends from the riser 8 to one end of the horizontal supply pipe 3, the other end of this pipe 3 having communication with a receptacle 1.

An auxiliary supply pipe '6 extends upwardly from the horizontal supply pipe 3 and supplies water to other plumbing fixtures (not shown).

In Figure 1 of the drawings, I have'illustrated the arrangement for one of the lower floors and the same arrangement of piping is employed with all of the other lower floors.

The auxiliary supply pipe 6 being in the instant case, the highest branch of the supply pipe 3, therefore the loop 3-B must be higher than the height of the auxiliary-supply pipe 6. The height of the loop or branch supply conduit 3B is indicated by hi and-the height of the auxiliary supply-pipe 6 is designated by "114. The water column in excess to hi is indicated by hz. It will thus be seen that the height of the loop or branch supply conduit 3-3 is equal to hi plus hz.

The hydrostatic pressure head created by the height of the branch supply conduit or loop 3B, above the normal water level in the receptacle 1 is greater than the maximum suction that is possible to be produced at the point of communication of the upper end of the conduit or loop 3B with the riser 8.

Considering the very fact that the pressure being always the smallest at the top floor, in any up-feed or down-feed riser, consequently the pressure will cease at the top fioor first, and only after this will the pressure gradually cease at the lower branches in case of a total pressure drop regardless of the cause of its occurrence (shutting olf the main or overloaded or corroded supply riser, poor pressure conditions, etc.). In the referred case of a total pressure drop the prevailing hydro-static pressure between floors will cause a flow toward the supply pipe 3 and downward in riser 8 depending on the size of riser and size of supply pipes at the lower floors, and depending also on the rate of flow, in this case on rate of reverse flow.

In a case of a total pressure drop the down falling water column will be followed by the atmospheric air passing through extended air pipe [0 or through atmospheric air supply inlet into the riser 8, and as stated before, always with such velocity as the velocity might be of the down falling water column in riser 8. The branch supply conduit 3-3 as indicated, being considerably higher than the auxiliary supply pipe 6 and higher than the maximum water-line in receptacle I therefor, the supply-branch outlet connected to riser 8 must be always free from the slightest obstruction and due to this the inflowing atmospheric air will exert its pressure on the surface of water in branch supply conduit just the same as the same atmospheric pressure exerts its pressure on the surface of the water in receptacle 1 and in auxiliary supply pipe 6 which might be open to atmosphere due to an open faucet, etc.

If the water column in the riser 8 drops with a velocity which is sufficient to create suction at the inlets to the respective several branch conduits, the head of the water column in the liquid seal l and the loop 3b is arranged to be of a sufficient height to prevent reverse flow from such inlets into the riser. The friction and resistance which would be produced if there were any reverse fiow could also be taken into consideration in determining the necessary heads of water columns in the seal and loop.

The air pipe I0 can enter into an air supply header which again ends at such place at the upper part of the building where an unobstructed free air supply can be easily secured or pipeline I!) might end into a well protected air-supply inlet head protected with a carefully secured and enlarged wire screen having at least four times as large cross section as the pipe-line it in order to eliminate the slightest resistance at the source of atmospheric air supply, as shown in my prior Patent No. 2,205,305. Of course, the applied method of atmospheric air supply into riser 8 depends entirely on local building and prevailing pressure conditions, namely, the method of atmospheric air supply into the riser 3 is entirely different from a riser which ends at the-fifth floor-ofa thirty (30) story high build ing or theriser 8 ends at'the thirtieth floor of the same building, or is the top of the riser (pipe H] of the water seal of Figure 1), occasionally"- below orabove'the prevailing pressure zone. The

height of the conduit 3- B is to be determined by local conditions when the height and volume of riser 8 has to be" considered andalso" the maximumvelocity of the down falling water column (based on the Newton theorem) in a case of a total pressure drop in riser 8 especially; when the riser 8 has to be drained in which case the velocity of the down falling-water column might reach its maximum velocity), and so the velocity of the inflowin-g atmospheric air.

The purpose of Fig: 2 is' to clarify the pressure and airflow conditions at the lower floors of a riser 4, which is provided with a water seal at the top outlet of the riser4,'in order to elimi-' nate the remotest possibility of reverse flow from any plumbing fixtures; etc., supplied with water through the water seal l'. seal-at the top floorwill create that hydrostatic pressure in shell H in a case of a total pressure drop, which-hydrostatic pressure is absolutely that the same prevention of'reverse-flow hasbeensuccessfully established nor achieved at the lower floors of the same riser 4, orany other riser in the same building regardless that those risers are supplying hot or cold water for human consumption.

According to the standard piping practice. in buildings the supply branches at the lower floors are arranged in the floor construction, concealed in order to eliminate door and window crossings, as is clearly indicated in Fig. 2. The supplybranch 3 supplies the receptacle 1 with hot or cold water and the auxiliary supply pipe 6 which leads, as usually to a shower or to any other plumbing fixture (not shown). The height of the maximum water-line of receptacle 1 is indicated by its and the height of auxiliary supply-pipe 6 and maximum water level is indicated by hi. In a case of total pressure drop in riser 4, the hydrostatic-pressure existing between the top of riser 4 and between the supply branch (takeoff) 3 will cause a flow of water toward the receptacle 1 and auxiliary supply pipe 6. This flow will continue until the motive power of flow, namely, the previously referred hydrostaticpressure exists between the upper and lower supply pipes, ior example, between the submerged top of the water seal I and between supplybranch 3.

Installing a Water- Of course, in determining such necessary heads,

consideration may be given to pressure drop'dueto friction and resistance existing in the-branchesand their take-offs.

Having thus described my invention, what I claim is:

l. In a vertical water supply system, wherein a plurality of receptacles having a normal liquid level, are disposed at different levels and connected to a common liquid supply riser, means for-supplying liquid to those receptacles below the uppermost'receptacle including a branch leading into" each receptacle from the supply v riser from a point in said supply riser above the normal liquid level in each receptacle, the height of the branch above the normal liquid level in said lower receptacle being such as to produce .a head greater than the. maximum suction head capable of being produced by the velocity of flow of fluid in the riser at the point of take-offconnection between the branch and the riser, a shell surrounding and spaced from the upper portion of the riser and communicating at its upper end with the atmosphere and closed at its lower end, a branch connecting the upper most receptacle with the shells, the upper end of the supply riser being open and extending above the normal liquid level in the uppermost receptacle, the height of the riser. above the, upper receptacle being sufficient to create a head of liquid in the shell capable of preventing reverse fromv said last mentioned branch'to the shell as a result of a maximum drop inpressure in theriser at the point of take-01f of said branch due to velocity flow of fluid past said take-off.

2. In avertical water sup-ply system embodying a plurality of receptacleshaving anormal liquid level, adapted to be-supplied and wherein the receptacles are disposed at different levels, a liquid supply riser, closed branches leading respectively from said riser to each of the lower receptacles from a point substantially higher than the highest normal liquid level in each of the lower receptacles, the height of the branches above the normal liquid level in each of said lower receptacles being greater than the maximum suction head capable of being produced by the velocity of flow of fluid in the riser at the point of take-01f connectionbetween the branches and the riser, a branch connecting the uppermost receptacle with the supply riser, the upper end of the riser being open and extending above the normal liquid level in said uppermost receptacle, and a liquid seal for the last mentioned branch including a surrounding spaced shell about the open upper end portion of the riser, said shell having its upper end venting to the atmosphere, the lower end of the shell being closed, said last mentioned branch having communication with the lower portion of the shell, the height of the riser above the normal liquid level in the uppermost receptacle being sufficient to create a head of liquid in the shell capable of preventing reverse flow from the last mentioned branch to the shell as a result of a maximum drop in pressure in the riser at the point of take-off of said branch due to velocity flow of fluid past said take-off, whereby reverse flow of the liquid into the riser from the receptacles is prevented.

3. In a vertical water supply system, wherein a plurality of receptacles having a normal liquid level are disposed at different levels and connected to a common liquid supply riser, means branches =-which is greater than the greatest possible sub-atmospheric pressure at the" take-cits.

for supplying liquid to those receptacles below the uppermost receptacle including a branch leading into each receptacle from the supply riser from a point in said supply riser above the normal liquid level in each receptacle, a shell surrounding and spaced from the upper portion of the riser and communicating at its upper end with the atmosphere and closed at its lower end, a branch connecting the uppermost receptacle with the shell, the upper end of the supply riser being open and extending above the normal liquid level in the uppermost receptacle, the height of the riser above the upper receptacle being sufiicient to create a head of liquid in the shell capable of preventing reverse from said last mentioned branch to the shell as a result of a maximum drop in pressure in the riser at the point of take-off of said branch due to Velocity flow of fluid past said take-off, the vertical distance of each of the first mentioned branches above the normal liquid level of their associated receptacles and their point of connection with the riser as well as the height of the riser above the uppermost receptacle being equal to a head sufficiently higher than the head produced by the maximum suction capable of being produced at each branch connection as a result of any pressure drop in the riser, minus the head due to pressure drop caused by friction and resistance in the branches if reverse flow could occur therein, whereby reverse flow of liquid'back to the supply riser is prevented.

4. In a water supply system embodying a plurality of receptacles having a normal liquid level, and wherein the receptacles are disposed at different levels, a liquid supply riser having its upper end in communication with the atmosphere, means for delivering liquid from the supply riser to said receptacles including branches, each of the receptacles including a back siphonage prevention means, the back siphonage prevention means for any selected receptacle being formed by arranging the branch so as to lead from the supply riser at a point substantially higher than the normal liquid level in the selected receptacle, the efifective height of each branch from its connection between the riser and the normal liquid level of its associated reoeptacle being sufficient to overcome the maximum suction head capable of being produced by the velocity of fluid passing the point of take- Off connection between the riser and the branch for such receptacle due to pressure drop in the riser, whereby reverse flow of liquid back to the supply riser is prevented. V

5. In a water supply system embodying a plurality of receptacles having a normal liquid level, and wherein the receptacles are disposed at different levels, a liquid supply riser having its upper end in communication with the atmosphere, means for delivering liquid from the supply riser to said receptacles including branches, each of the receptacles including a back siphonage prevention means, the back siphonage prevention means for any selected receptacle being formed by arranging the branch so as to lead from the supply riser at a point substantially higher than the normal liquid level in the selected receptacle, the vertical distance of each branch above the normal liquid level of its associated receptacle and its point of connection with the riser being equal to a head sufiiciently higher than the head produced by the maximum suction capable of being produced at each branch connection as a result of any pressure drop in the riser, minus the head due to pressure drop caused by friction and resistance in such branch if reverse flow could occur therein, whereby reverse flow of liquid back to the supply riser is prevented.

LOUIS IRVING NORTHON. 

